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Chemical synthesis of phytosterol esters of polyunsaturated fatty acids with ideal oxidative stability



In this study, direct esterification of phytosterols with polyunsaturated fatty acid (PUFA) catalyzed by sodium bisulfate to produce sterol esters of PUFA was performed without organic solvent. Considering on both degree of esterification (DE) and oxidative stability, response surface methodology (RSM) was employed for modeling the phytosterol esters of PUFA production to obtain a food grade process. The optimal and mild reaction conditions were obtained as follows: mass ratio of PUFA:phytosterols = 4:1; amount of catalyst: 3% of the raw materials weight; reaction temperature 130°C; reaction time 8 h. Under these conditions, the degree of esterification was up to 96%, GC, TLC, NMR and GC-MS results showed that purity of purified sterol ester was above 99%, and β-sitosterol linolenate account for about 88%. Sterol ester of PUFA possessed low peroxide value (PV) (0.96 meq/kg) and conjugated diene (CD) value (2.15 mmol/kg), and high oxidative induction period (OIP) (10.4 h). Addition amount of sterol ester of PUFA into soybean oil, rapeseed oil, and flaxseed oil below 1, 1, and 3%, respectively, could increase OIP of the vegetable oil. The primrose phytosterol esters of PUFA possessed very low melting point, crystallization temperature, and greater solubility in oils. All the characteristics favored the wide application of sterol ester of PUFA produced by the food grade process in different formulations of functional foods.